In the present of high energy consumption in every sphere of life, renewable energy sources are emerging as alternative to conventional fuels for energy security, mitigating green house gas emission and climate change. There has been a world wide interest in searching for alternatives to petroleum derived fuels due to their depletion as well as due to the concern for the environment. Vegetable oils have capability to solve this problem be cause they are renewable and lead to reduction in environmental pollution. But high smoke emission and lower thermal efficiency are the main problems associated with the use of neat vegetable oils in diesel engines. In the present work, performance, combustion and emission characteristics of CI engine fuelled with 5% by vol. Diethyl Ether (DEE) mixed with Thevetia Peruvina Seed Oil (TPSO). Various performance, combustion and emission characteristics such as thermal efficiency, and brake specific fuel consumption, volumetric efficiency are measured and results are revealed that 5% DEE mixed with biodiesel gives improved performance, combustion and emission characteristics.